Dropping boost at high RPM? Help

[xkalelx]

Calling all turbo gurus! This is my first turbo car. Looking for some input.

Its going to be a LONG weekend for me, my car is out of town at a very reputable dyno tuning shop and they are having some issues with my car.

Cliff notes of my build: stock block, 6MT, 6758 EFR turbo, 700cc DW inj, DW 300 pump, flexfuel, EcuTec. Was on Delicious Flash&Go for about 3 months following the turbo install. Nothing against Zach or Bill, but I think we got it as close as it was going to get without actually rolling it on a dyno. Was having very frustrating idle hunting, stalling and low throttle hesitation.

So I dropped the car off Tuesday evening to get a full dyno tune on 93 and e85. Full day of tuning Wednesday yielded weird boost readings while just on wastegate pressure. Inconsistent boost building and bad boost droop. See dyno sheet below. We were both thinking it was the wastegate actuator so I overnighted a new Turbosmart 10psi wastegate actuator. Thursday was already scheduled for another client, mine went back on the dyno today around lunch and the new actuator didnt fix the problem (I hate throwing money at problems). So by the end of today, still dont have any idea what is causing this issue. Monday morning hopefully we will find out more.

Dont want to call the shop out, they've been great so far. Just here looking for information.

TIA!

Sam

[NahumCC]

Have you made sure any silicone tubing routing air into the compressor side isn't collapsing under vacuum? If it's not heavy duty reinforced tubing it could be collapsing under load creating a flow restricrion.

Next thought is if there is any pinging or knock occuring? When they had it on the dyno to tune were they seeing any knock indicators to show why the ECU may be dumping the boost or advancing the timing?

Just food for thought from 10 years on playing with SAABs.

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[xkalelx]

I appreciate the input @NahumCC. Those are excellent theories. All of the charge piping and intake have very close fitups (1/8-3/16" gaps). So having a silicone collapse would be impossible. And I am not sure if my tuner is seeing any knock. He's about 2 hours drive from me and his lead tech gives me pretty frequent updates but i don't know specifics like that.

I'm wondering if this is a flow issue. They mentioned looking at the recirculation valve (BOV located on the compressor housing) Monday morning. My brain is fried. The obvious boost leak is not there and no vacuum leaks either.

[NahumCC]

Originally Posted by xkalelx

I appreciate the input @NahumCC. Those are excellent theories. All of the charge piping and intake have very close fitups (1/8-3/16" gaps). So having a silicone collapse would be impossible. And I am not sure if my tuner is seeing any knock. He's about 2 hours drive from me and his lead tech gives me pretty frequent updates but i don't know specifics like that.

I'm wondering if this is a flow issue. They mentioned looking at the recirculation valve (BOV located on the compressor housing) Monday morning. My brain is fried. The obvious boost leak is not there and no vacuum leaks either.

Not sure what you mean by the gaps as close fit ups unless that's where you are placing the clamping bands.

What I was trying to get at is maybe it's that the steel bands within the layers aren't strong enough to keep a collapse from happening on t he intake hose to the compressor inducer.

You tuner has a good point to take a look at the diaphragm of the integral BPV on the compressor housing (can't see it from the picture).

Another thought I had was how are you controlling the wastegate? Spring and Ball MBC or a EBC? If MBC then maybe the spring is to weak. If EBC, then may need to check power to it and it's mapping (if it's fancy enough to be integrated with the ECU).

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[NahumCC]

Also, is the integral BPV pneumatic or electronic solenoid?

If pneumatic it needs a signal line to keep pressure pushing down onto the BPV and vacuum to pull it open quickly. Best tap location is the manifold after the throttle body because it's internal spring should be strong enough till the total intake volume is charged but as soon as you cease the boost demand you want the quickest vacuum pull to open it and prevent a compressor stall.

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[xkalelx]

The charge piping and intake are aluminum. All of the piping was fabricated to be very tightly fit up so just slip silicone couplers and hose clamps could be used. There are no silicone hoses or elbows. All of the clamps are tight. No boost leak in the charge piping or FMIC.

Wastegate is controlled for the stock EFR Pierburg EBCS. Harnessed to the EVAP connector and my AEM Failsafe. My tuner can't get consistent pulls on just wastegate pressure so he hasn't begun dialing in electronic boost control. I guess the former has to come before the latter.

The recirculation valve is pneumatic. It gets plumbed to a vacuum line off of my brake booster hose.

[xkalelx]

@NahumCC

[NahumCC]

Sounds then that once the EBC is dialed in you'll be fine. Your basically running a linear push signal from the compressor to the wastegate. The modulation is needed from the EBC to keep the wastegate shut.

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[xkalelx]

I get that, that makes sense. But if you have a 10psi spring in the WG and you leave the EBCS unplugged. You should be able to hit 10psi and maintain it just off the wastegate alone. Im only making 4psi at redline with a 10psi spring so something has to be off.

Im putting my faith in this tuner who tuned 15 FRS/BRZs last month alone and is a EcuTek and Haltec master tuner. Im trusting he knows his shit, Im just so confused by this symptomatic issue. (Im sure he is pulling his hair out as well being almost 2 full days in already).

[NahumCC]

You also have to consider the volume of exhaust and flow rate (the a/r ratio of the turbine housing) at the rpm where the wastegate spring isn't keeping up. PV=nRT says if the volume the exhaust dumps into remains the same and if T (EGT in this case) and n (mols of air) are increasing that P (pressure) has to climb leading the wastegate to blow open in the lack of a control source to counter that force.

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[Toyarzee]

Internally gated turbo and the bov is right at the turbo housing as well? Sounds like an interesting flow design... Subbed to see outcome. This is y I always go external wg and vent bov. It sucks being on a dyno and having to take her down for work, been there several times and I feel your pain. Gl man

[xkalelx]

Originally Posted by NahumCC

You also have to consider the volume of exhaust and flow rate (the a/r ratio of the turbine housing) at the rpm where the wastegate spring isn't keeping up. PV=nRT says if the volume the exhaust dumps into remains the same and if T (EGT in this case) and n (mols of air) are increasing that P (pressure) has to climb leading the wastegate to blow open in the lack of a control source to counter that force.

I can almost follow that but I wont pretend to know what all that means haha. I know I have a .64AR turbine housing. I thought maybe I have an exhaust restriction since I dont have a full 3" exhuast. But I have a 3" downpipe to an Invidia OP (60mm) to Invidia resonated FP (60mm) and Invidia N1 (60mm). No cats. No exhaust leaks. All new gaskets.

Originally Posted by Toyarzee

Internally gated turbo and the bov is right at the turbo housing as well? Sounds like an interesting flow design... Subbed to see outcome. This is y I always go external wg and vent bov. It sucks being on a dyno and having to take her down for work, been there several times and I feel your pain. Gl man

Thanks! The EFR has been out for a couple years but is a tried and true design. Pretty wizbang turbo technology. Titanium aluminide rotor, dual ceramic ball bearings, oil fed, water cooled, forged milled compressor wheel, IWG, integrated BOV, integrated EBCS, cast stainless turbine housing, and even a location for compressor wheel speed sensor. Very high end stuff here. Also available with EWG and twin scroll.

[Kenneth]

The yellow boost line looks good. A bit of overshoot on spool, followed by flat boost and then it tapers off most likely due to exhaust pressure being high, making it harder to keep the wastegate closed.
This is what I would expect to see on a car with small turbo(s) and a MBC.

If you can make it do that all the time, nothing is wrong and you need some boost control.

Blue looks to be wastegate pressure only and the other 2 could be due to EBC not being setup well.


If you want to diagnose problems, first do a boost pressure test to make sure the intake is holding pressure. IMO, its critical in a turbo system to ensure everything holds pressure, if there are any leaks you can waste countless hours trying to look for a problem which doesn't exist.

Next, bypass the EBC and connect the compressor outlet pressure directly to the wastegate.
It looks to be easily accessable from your picture so should be easy to do.
You should watch the wastegate actuator arm and ensure it is moving as expected during the dyno pull to verify that its working properly.

If this fixes your problem, your EBC could be connected incorrectly or faulty (or just programmed badly)

If not, you need to look at the pressure bypass valve to make sure it is correctly connected (as suggested above) to the engine side of the throttle body. This needs pressure to keep it closed, without this pressure feed the boost pressure will push it open, leaking the boost.
This means if it is either not connected, or connected badly with a hose which sometimes blocks/kinks you will not get good boost control.

Those are the most likely reasons for poor boost regulation.

If that doesn't get you where you want to go, you will need to provide more information. Namely data logs which will show AFR, timing, knock correction etc.

[NahumCC]

Originally Posted by Toyarzee

Internally gated turbo and the bov is right at the turbo housing as well? Sounds like an interesting flow design... Subbed to see outcome. This is y I always go external wg and vent bov. It sucks being on a dyno and having to take her down for work, been there several times and I feel your pain. Gl man

Actually, if you look since about the mid 2000's you'll see the integral BOV as part of the compressor housing has been around on the common factory turbo's from Garrett and Mitsubishi in larger numbers.


The benefit of having moved the BPV into the compressor housing goes to the point above when I mentioned the vacuum signal to pull open the BPV should always be after the throttle body in the intake plenum. Having the BPV in the compressor housing puts it closest to the source where any compressor stall would do the most damage and provide the most beneficial path of least resistance.